Would any one else buy a graphics card that used an external power supply. Like instead of going through the cost and trouble of upgrading your power supply just to use a better graphics card, it came with something like a power adapter that just plugged into the back of the graphics card.
Small power supplies are going to be much less efficient, run hotter, and probably result in poorer quality power since they wont necessarily have to meet ATX specs. Can you link to an example of a card with something you are talking about or is this a theoretical question?
There are small power supplies that fit in 5.25" drive bays which are meant to provide the additional power for a graphics card but they are reasonably expensive and hard to find.